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Nitrogen and organic carbon of soils as affected by crops and cropping systems

Metzger, W.H.
Agronomy journal 1936 v.28 no.3 pp. 228-233
animal manures, Triticum aestivum, Medicago sativa, Zea mays, Vigna unguiculata, crop yield, soil analysis, Glycine max, nitrogen, carbon, crop rotation, continuous cropping, Kansas
Studies have been conducted at the Kansas Experiment Station to determine the effect on the soil nitrogen and organic carbon of the following crops and cropping systems: Wheat continuous, alfalfa continuous, a 3-year rotation of corn, cowpeas (or soybeans), and wheat, and a 16-year rotation in which alfalfa is grown for 4 years and a 3-year rotation of corn, wheat, and wheat takes up the remaining 12 years. Corn was indicated to be much more destructive of nitrogen and carbon than any other crop or cropping system. Both alfalfa and cowpeas appear to have added to the soils nitrogen supply, but the latter was more destructive of carbon than the former. Continuous wheat produced about the same effect as each of the two rotations. Total crop production over a period of 25 years and total nitrogen of the soil were shown to be highly and positively correlated. Manure applications failed to produce significant increases of nitrogen or carbon which could be attributed to the manure and not to increased crop residues. The nitrogen of the soil of the experimental plats studied appears to be definitely approaching an equilibrium characteristic of the crop or cropping system employed.